What lactation consultants need to know about thyroid function and milk supply

Thyroid Function and Milk Production: What a Lactation Consultant Needs to Know

1. Why the Thyroid Matters for Lactation

• The thyroid gland regulates metabolism and energy through hormones: mainly T3 (triiodothyronine) and T4 (thyroxine).
• It’s under the command of the brain (pituitary and hypothalamus) via TSH (thyroid-stimulating hormone).
• For lactation, thyroid hormones help regulate prolactin and oxytocin activity, and influence energy balance.
• If thyroid function is off—either too low (hypothyroidism) or too high (hyperthyroidism)—milk production can suffer.

Key points:

• Hypothyroidism = Common cause of low milk supply
• Hyperthyroidism = Can cause oversupply initially, but then crash supply due to metabolic exhaustion.

2. Common Thyroid Conditions Seen in Lactating Parents

• Primary Hypothyroidism (Hashimoto’s, iodine deficiency)
• Subclinical Hypothyroidism (mild TSH elevation, normal T4)
• Postpartum Thyroiditis (inflammatory, can swing from hyperthyroid to hypo)
• Graves’ Disease (less common but significant hyperthyroidism)

3. What Labs Should Show

When a client reports low milk supply with fatigue, hair loss, cold intolerance, weight changes, constipation, mood changes, or feels like something is “off,” you should be thinking thyroid.

If bloodwork is ordered, key labs:

Notes:

• High TSH + low Free T4 = primary hypothyroidism (often needs treatment)
• Normal TSH but symptoms? Consider stress, nutrition, subclinical hypothyroidism, or check free T3/free T4.
• Positive TPO antibodies = high risk for developing full hypothyroidism later, even if TSH looks okay now.

Red flags for lactation consultants:

• TSH > 2.5 postpartum + supply issues = medical referral needed
• Free T3 or T4 low = referral and discussion with MD or endocrinology

4. Nutrition’s Impact on the Thyroid

Certain nutrients are critical for healthy thyroid function—and for making enough milk:

Deficiencies (especially iodine, iron, selenium) are super common postpartum and can directly impair thyroid health—and thus milk production.

Note:

The RDA for iodine increases to 290 mcg/day in lactation, and most prenatals don’t cover this well.

5. Stress and Thyroid Health

• Chronic stress (physical, emotional, lack of sleep) impacts the hypothalamic-pituitary-thyroid (HPT) axis.
• Cortisol (stress hormone) can suppress TSH temporarily and block T4 → T3 conversion, causing “low T3 syndrome” without true hypothyroidism.
• Stress can mimic thyroid dysfunction or worsen underlying mild issues.
• Stress also affects prolactin and oxytocin directly, making lactation even harder if thyroid function is struggling.

6. When to Suspect Thyroid Issues in Lactation

• Low or dropping milk supply despite good management
• Baby not gaining well despite frequent feeding
• Maternal symptoms: fatigue, depression, constipation, weight gain/loss, cold hands, brittle hair
• Difficult letdowns or supply that seemed fine, then mysteriously drops around 6–12 weeks postpartum
• Previous thyroid problems, history of infertility, or autoimmune disease

Always remember:

Milk supply is not only mechanical—it’s hormonal and metabolic too.

7. How to Support Clients (As an IBCLC or LC)

• Validate: “It’s not just you. Let’s make sure your whole body is being supported.”
• Encourage gentle nutrition: focus on whole foods, enough calories, iodine-rich foods, protein
• Encourage rest when possible (yes, easier said than done)
• Recommend thyroid testing if symptoms + low supply
• Collaborate with providers (midwife, OB, endocrinologist)
• Support lactation with hand expression, pumping, skin-to-skin, responsive feeding while underlying issues are addressed

TL;DR: Quick Cheatsheet

• Thyroid hormones = critical for lactation
• Hypothyroid = low supply risk
• Key labs: TSH (ideal 1–2.5), Free T4, Free T3, thyroid antibodies
• Watch for nutritional gaps (iodine, iron, selenium)
• Chronic stress can mimic or worsen thyroid issues
• Trust your instincts when something “doesn’t add up”—a sleepy or fussy baby, slow weight gain, and a drained, symptomatic mom need a deeper look.